Generally speaking, there is a desire for illumination devices that are capable of generating light with a variable light intensity (dimming) and variable color. As should be clear to a person skilled in the art and therefore needs no elaborate explanation, it is possible to generate light of all possible colors in a large portion of the color gamut with an arrangement that comprises three primary LEDs generating light of mutually different colors. In a typical example, one LED generates RED light, a second LED generates GREEN light, and a third LED generates BLUE light. The combined light output of these three primary LEDs has a mixed color within the color triangle defined by the colors of these three primary LEDs, and the exact color point within this color triangle depends on the mutual ratios of the intensities of the three primary LEDs. Thus, varying the color point of the arrangement can be done by changing the relative intensity of one of the three primary LEDs, whereas varying the intensity of the light output while maintaining the color point can be done by changing the intensities of all primary LEDs to the same extent.
It is noted that it is possible to use more than three primary LEDs with mutually different colors; in such case, the present invention can also be applied, with suitable adaptations, as will become clear to a person skilled in the art.
In the following, a basic assembly comprising three (or more) different primary light sources will be indicated by the phrase “spot”. Thus, in its smallest implementation, a spot comprises exactly three LEDs. However, it is possible that a primary light source is implemented by an array of mutually substantially identical LEDs, each generating substantially the same color, which are connected in a parallel and/or series arrangement to increase the light output. In the following, it will be assumed that each primary light source is implemented by one LED.
For controlling the intensities of the respective primary light source, a spot is provided with a microcontroller. The microcontroller has an input for receiving a set signal, for instance from a central microcontroller or PC. The microcontroller further has three control outputs, one for each LED, for controlling the operation of the respective LEDs. Typically, the LEDs are operated with a variable duty cycle to achieve variation of the respective light intensities.
An illumination system may comprise two or more spots which should be operated in the same way, i.e. produce the same light color and intensity level. Thus, with increasing number of spots, the number of microcontrollers also increases. This poses a problem in terms of costs, since the microcontrollers are the major cost factor in a spot.
The present invention aims to overcome this problem. More specifically, the present invention aims to provide a relatively simple and low-cost illumination system comprising two or more spots, which can operate with only one single common controller.